<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>背景透明写法</title> 
    <style>
        div {
            width: 300px;
            height: 300px;
            background: rgba(0, 0, 0, 0.1);
        }
    </style>
</head>

<body>
    <div>隐形的翅膀</div>
</body>

</html>